Formed strap frame grid



March 24, 1964 F. c. REID 3,126,496

FORMED STRAP FRAME GRID Filed Dec. 21, 1961 2 Sheets-Sheet 1 ENTOR Freda 0. Reid TORN EY March 24, 1964 c, E 3,126,496

FORMED STRAP FRAME GRID Filed Dec. 21, 1961 2 Sheets-SheetZ TTORN EY United States Patent Ofi ice 3,126,496 Patented Mar. 24, 1964 3,126,496 FORMED STRAP FRAME GRID Frederick C. Reid, Emporium, Pa., assiguor to Sylvania Electric Products Inc., Emporium, Pa., a corporation of Delaware Filed Dec. 21, 1961, Ser. No. 161,169 3 Claims. (Cl. 313348) This invention relates generally to electron discharge devices and more particularly to a grid of the strap frame type useful in an electron discharge device.

In grid structures of the strap frame type, a common and frequently used structure provides circular side members held in spaced relationship by spaced cross straps and wound with a helix of lateral wire which is in frictional engagement with the central or window portion of the side members. Although this structure is satisfactory in some applications, the demand for higher amplification devices has necessitated an increase in the number of lateral wire turns and a decrease in the electrode spacing with resulting grid frame problems. It has been found that an increase in the number of grid laterals tends to cause the circular side members to bow inwardly during sustained periods of operation with a resultant change of electrode spacing. In addition, the prior art fails to provide means for altering the electrode spacing other than by changing the overall side member diameter. Any change in size or shape of the end portions of the side members also requires a change in the insulator aperture size into which these side members are inserted and firmly held.

Co-pending application, Serial No. 104,404, filed April 20, 1961, and owned by the Assignee, provides a structure which increases the side member resistance to inward bow and also provides an economical method for altering the electrode space relationships. Though this structure is a very useful advance over the prior art, in some applications it has been found that sustained periods of operation in electron tubes result in a rotation or twist of at least a portion of the flattened or rectangularly shaped side members about their longitudinal axes and a change in grid minor dimension spacing. Therefore, it would be desirable to provide a grid frame structure with side members which have an increased resistance to inward bow, and which provide a minimum distortion of the grid minor dimension due to temperature induced side member twisting.

It is an object of this invention to insure maintenance of the electrode spacing during sustained operational periods of an electron discharge device.

Another object of this invention is to provide increased reliability during operation of an electron discharge device.

A further object of this invention is to provide increased resistance to inward bow of the electrode side members during operation of the discharge device.

A still further object of this invention is to provide a minimum grid minor change for a given longitudinal rotation of the grid frame side members.

For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 is a front elevation of a strap frame grid electrode with shaped side members and upper and lower cross straps attached thereto forming an internal window;

FIG. 2 is a cross-sectional view along a line 22 of a shaped side member shown in FIG. 1;

FIG. 3 is a plan view of a side member showing the shaped central portion and the dimensionally difierent outer portion;

FIG. 4 is a front elevation of another embodiment of a strap frame grid with shaped side members and cross straps forming an internal window; and

FIG. 5 is a cross-sectional view along a line S5 of the shaped side member shown in FIG. 4.

In the drawings, FIG. 1 illustrates a strap frame grid electrode suitable for use in an electron discharge device or vacuum tube. In a strap frame grid structure 7, spaced side members 9 having an internal shaped portion 11 and an outer portion 13 are held rigid by attached cross straps 15 forming an internal grid window 17. The internal shaped portion 11 of side members 9 is wound with a helix of lateral wire 19. The rectangular perimeter of the cross straps 15 and shaped side member portions 11 provides the limiting dimensions of parallel lateral wire planes separated by the thickness of the shaped side member portion 11. This thickness dimension is normally defined as the grid minor and may be selectively altered during manufacture to adjust electrode spacing not only between the grid planes and the cathode but also between the grid planes and the anode. The lateral wire 19 is normally held in position through the major portion of turns by frictional engagement and attached by brazing, welding or notching, and peening at each end to one of the side members 9.

FIG. 2 shows a cross-section of the shaped side member portion 11 of side member 9 in FIG. 1. The shaped side member portion 11 provides a width dimension A perpendicular to and greater than the grid minor or thickness dimension B. The width dimension A is also greater than the original diameter of the circular side member C and thus provides an increased resistance to side member bow. Lateral wire sag and loss of tension is minimized allowing electrode spacing and the resulting tube characteristics to remain stable and reliable. Further, by shaping side member 9 as shown in FIGS. 1 and 2, grid minor dimensions, distortions, or changes are minimized under operating conditions which tend to twist the side members 9 around their individual longitudinal axes. Since the thickness or grid minor dimension B is established by upper and lower surfaces which are shaped convex outwardly, wherein each such convex surface has a radius of curvature substantially equal to one half the grid minor, the thickness or grid minor dimension is not changed as the side member rotates slightly about its own longitudinal axis. Obviously, even in the structures of FIGS. 1 and 2, if a side member rotates far enough, the grid minor will change. However, it has been found that the usual high temperature induced twisting of the grid frame side members is relatively small and the grid minor remains substantially constant during use. This is to be contrasted with grid frame side members of the type shown in the above-mentioned co-pending application, Serial No. 104,404, wherein the side members have a rectangular cross-section where grid, minor dimension change becomes a problem in some applications.

FIG. 3 shows a plan view of the side member 9 with cross straps 15 attached thereto. The internal shaped portion 11 and the outer portion 13 of the side member are shown to be dimensionally different. Thus the internal shaped portion 11 may be modified as to thickness and width-without change of the outer portion dimension 13. Since outer portions 13 fit into supporting mica apertures, this feature provides an economical method of electrode spacing or grid minor dimension alteration which does not require change of aperture sizes in the supporting end micas.

FIG. 4 is a front elevation view of another embodiment of the invention in which the shaped side member portions 21 provide a cross-section as shown in FIG. 5. This form of side member also has a width D which is prependicular to and greater than the thickness or grid minor dimension E. The configuration of FIGS. 4 and 5 also increases the resistance to side member bow. Further, the lateral wire spanning the side members is engaged and supported by the outwardly convex surfaces 27 which provide a minimum change in the grid minor dimension should any twist or rotation of the side member occur. Again, as was described with regard to the embodiment of FIGS. 1 and 2, the outwardly convex surfaces 27 of the side members have a radius of curvature which is substantially equal to one half of the grid minor dimension. Also, the outer portions 25 of side members 21 are round and unchanged regardless of change in grid minor dimension from grid to grid. Thus a grid supporting insulator of given aperture size may be used in a family of tubes, each with a different grid electrode to anode or cathode spacing.

In the process of fabricating strap grid frames with shaped side members 7, spooled side member material is progressively fed to shaping, Welding and severing stations. Adjacently spaced side member lengths 9 are simultaneously shaped, cross strap material is attached thereto and severed from its source, and the completed frame including cross straps and side members is severed from the side material source. The strap grid frame is then transferred to a strap frame grid winding machine for the addition of a helix of lateral wire. Although frame grid structures are normally made of molybdenum, this improved structure makes possible the use of plated steel or similar materials which are cheaper, more easily processed, and readily available.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein Without departing from the invention as defined by the appended claims.

What is claimed is:

1. In a frame grid the combination comprising a pair of side frame members held in spaced relationship by upper and lower cross straps to provide an internal grid window and a pair of parallel grid planes separated by a grid minor dimension defined by the projection of said internal side members on a plane normal to said grid planes, each of said side members having end portions of a given cross sectional shape and a central portion formed to provide a grid minor dimension which is substantially constant and at a minimum for a given number of degrees of rotation of the side member about its own longitudinal axis and which increases toward a maximum beyond said given number of degrees of rotation.

2. In a frame grid the combination comprising a pair of side frame members held in spaced relationship by upper and lower cross straps to provide an internal grid window and a pair of parallel grid planes separated by a grid minor dimension defined by the projection of said internal side members on a plane normal to said grid planes, each of said side members having end portions of a given cross sectional shape and a central portion formed to provide a grid minor dimension which is substantially constant for a given number of degrees of rotation of the side member about its own longitudinal axis and which increases toward a maximum beyond said given number of degrees of rotation.

3. A frame grid having a given lateral wire minor dimension comprising a pair of similar side members held in spaced relationship by spaced cross members attached thereto, said side members having a cross-sectional area defining opposed end portion surfaces and opposed out wardly convex shaped portion surfaces located intermediate said end portion surfaces, said opposed shaped portion surfaces having a maximum distance therebetween equal to the distance between said opposed end portion surfaces, and a helix of lateral wire wrapped around said side members and engaging the shaped portion surfaces thereof, said convex shaped surfaces having a radius of curvature substantially equal to one-half the grid minor dimension.

References Cited in the file of this patent RCA Technical Note 200 (Cichoski: Vacuum Tube Grid Support Rods), Aug. 18, 1958. 

3. A FRAME GRID HAVING A GIVEN LATERAL WIRE MINOR DIMENSION COMPRISING A PAIR OF SIMILAR SIDE MEMBERS HELD IN SPACED RELATIONSHIP BY SPACED CROSS MEMBERS ATTACHED THERETO, SAID SIDE MEMBERS HAVING A CROSS-SECTIONAL AREA DEFINING OPPOSED END PORTION SURFACES AND OPPOSED OUTWARDLY CONVEX SHAPED PORTION SURFACES LOCATED INTERMEDIATE SAID END PORTION SURFACES, SAID OPPOSED SHAPED PORTION SURFACES HAVING A MAXIMUM DISTANCE THEREBETWEEN EQUAL TO THE DISTANCE BETWEEN SAID OPPOSED END PORTION SURFACES, AND A HELIX OF LATERAL WIRE WRAPPED AROUND SAID 